Announcement

Collapse

Help Tip: If you have a question that has not been answered to your satisfaction in the archives, it is always best to start a new thread of your own. By starting your own thread, you will receive the maximum number of views by forum members.

Below are some additional forum policies in hopes of all iboats members will follow, Thank you.

1. Please do not reply to old topics or hijack existing topics. Old topics of a technical nature are like a library book, Please do not write in them.

2. Old topics should be considered archives and used for reference only. Please do not reply to them.

3. Do not take over someone elseís topic (aka hijack) with your own question, even if it is similar. If you have a question that has not been covered to your satisfaction in the archives, it is always best to start a new topic of your own.

4. If you have a question for the original poster (OP) and the topic is over 30 days old, send the OP a PM, he may not even visit the forums any longer, or may not notice your question in the old topic.

5. By starting your own topic, you will receive the maximum number of views by forum helpers that may not even notice your question when itís posted at the end of someone elseís topic. And those answers will be specific to your particular issue.

6. Please do not post to topics that have been inactive for more than 3 months unless you are the original poster. We have very active forums and any topic that remains inactive for that long should be considered "dead". It is especially confusing when there is an entirely new question posted to an old topic.

7. Posting at the end of any topic is considered to be hijacking the original posters topic which in turn subjects the topic to be closed if it continues to happen thus not making it fair to the original poster in the future had for some reason he/she needed to return for additional information or provide an update of the problem solved which is always welcomed within a reasonable amount of time frame.

8. Please note that you should see a red banner pop up near the bottom of each inactive topic asking you not to reply to old topics. The Red banner will read: Please note this topic has been inactive for 90 days. For the best results, please start a new topic.

Thank you all in advance for doing your part in helping iboats run a smooth ship.

Ok, so I bought my first boat in April. It is a 1972 Larson Trihull with a Mercury 850 attached. I have taken the boat out approximately 5 times since I purchased it and it has ran like a champ until yesterday.

It started up and idled great. It went into gear and ran moved nicely across the water. As soon as I crossed the no wake zone, I ran into issues. I put the throttle approximately 3/4 of the way down. The motor started to go, but then fell flat on its face. It would not move at all. It wouldn't open up and I could only go approximately 10 MPH. It kept bogging down.

I puttered around the lake for 5 hours, mainly fishing, and then brought the boat home. The whole time on the lake it bogged down going more than 1/2 to 3/4 throttle, but ran like a champ below 3/4 throttle. At home, I ran it on muffs and it ran like a true champ (even at full throttle). It did not bog down at all while on the muffs. I thought maybe it fixed itself, ya right. So, just in case it didn't fix itself I went to the local marina and got some suggestions.

After speaking with them, I came back home and I ran a compression test. I got 115 PSI in each of the cylinders. I then went out and bought some BG fuel additive (suggested by my Marina) and x4 new spark plugs. I added the BG additive to 6 gallons of fuel (nearly double the suggested amount) and changed all of the spark plugs. I was feeling confident that this may solve the problem, so back to the lake I go.

At the lake, it started and idled just fine. I got past the wake zone and got similar results. This time it seemed to go a little faster, but still the bogging issues. I figured I needed to run the entire tank through the engine to clean it out (with the BG additive). While riding around, the engine would fluctuate and it seemed like it was going to take off, but it never did (it did this several times).

After I drained the first 6 gallons, I switched to my second tank. This time I disconnected the fuel filter (figured it maybe clogged) and ran fuel straight to the motor. Still no luck and lots of bogging and sputtering. We put the filter back on. I then had my friend pump the primer bulb while I got on it (the engine) and "boom" it seemed to take off. We did this several times and each time it seemed that pumping the bulb got the motor running correctly.

So, my question is this. Does that mean its a fuel pump issue? To my knowledge, it had never been re-built or replaced. If its the fuel pump, then why does it run perfectly while out of the water? Is there a way to test the fuel pump? What PSI should the fuel pump be putting out?

If it is the fuel pump, where can I find a replacement? What goes bad in them? I looked everywhere online and cannot find a place to by a new or used fuel pump for my motor. I believe my engine is a 1972 or 1973 Mercury 850 (85 HP), SN 7083192. The fuel pump has the #73433 etched on the top of it (probably a part number). Any help would be great. Thanks in advance.

Comment

Thank you very much. You are 100% correct about my motor being at 1976. I still don't understand how you got the year from reading my serial number, I looked at the above website and still cant figure it out. I appreciate you taking the time and responding to my post in such detail. Thanks.... I am going to order the diaphram kit.

Comment

I noticed that you ran it at full throttle on the muffs; don't run it above 1200 rpm when not under load!
If you have these carbs with the flattop there's a filter inside that might be plugged
remove them, unscrew the fuel fitting and look inside.
I had one that was full of lint.

Comment

I noticed that you ran it at full throttle on the muffs; don't run it above 1200 rpm when not under load!
If you have these carbs with the flattop there's a filter inside that might be plugged
remove them, unscrew the fuel fitting and look inside.
I had one that was full of lint.

I didn't run it very long with muffs on, but I will keep that in mind next time. I will check out my carbs and see if they are similar to the ones u posted.

Comment

ive had the same exact issues for all of last fishin season and tried alot of different things to no avail. i finally decided to take it to a mechanic. by the way i have a 1977 850 merc. anyway he ran some tests and found that my stator was bad. i havent replaced the stator because i now have a hole in the water jacket and am debating getting a newer year. hope this helps.

Comment

Well, today I received my fuel pump rebuild kit. It only cost me $5.00 and was very simple to install. While I was installing it, I noticed a thin fuel line leaking that runs from the bottom of the engine to the top of the engine. I don't know what it is for, but I replaced it with a new yellow fuel line. I will post some pics maybe someone can tell me what it does and what it's technical name is.

Comment

ive had the same exact issues for all of last fishin season and tried alot of different things to no avail. i finally decided to take it to a mechanic. by the way i have a 1977 850 merc. anyway he ran some tests and found that my stator was bad. i havent replaced the stator because i now have a hole in the water jacket and am debating getting a newer year. hope this helps.

Thanks for the post. If my latest updates (fixed leaking fuel line and rebuilt the fuel pump) then I will focus on the Stator. I want to rule out the cheap things first. Did the mechanic give you a quote on how much it would be for the part and labor?

Comment

That small rubber tube is the bleed system on your inline 4 motor. Any oil that pools on the lower main bearing is pumped thru that hose to the upper main bearing. Keep an eye on that yellow stuff you added, to make sure it holds up to fuel and temperature conditions in the motor.

Comment

That small rubber tube is the bleed system on your inline 4 motor. Any oil that pools on the lower main bearing is pumped thru that hose to the upper main bearing. Keep an eye on that yellow stuff you added, to make sure it holds up to fuel and temperature conditions in the motor.

I watched fuel move from the bottom connection up to the top connection, does it always bleed this way? I will keep an eye on the yellow hose, it was the only hose that i could find with a small size hole. The hose is a Holley and it made for fuel.